# What was the question to which Max Planck gave an explanation and how is it related to blackbody radiation?

Quoting from my text book - "several attempts were made to predict intensity as a function of temperature/wavelength". This line was preceded by the explanation for blackbody radiations and about how the intensity of radiation of a particular wavelength would be maximum at a particular temperature.

This was followed by "Planck gave a satisfactory relationship by assuming that absorption and emission of waves arises from oscillators I.e., atoms in the wall of the blackbody. He suggested that radiation could be sub divided into discrete chunks of energy, he gave the name quantum to the smallest quantity of energy that can be absorbed or emitted".

I am aware of the equation Energy=frequency x Planck's constant

How does Planck's above explanation correlate with intensity being a function of wavelength or temperature? How does it have a relation to blackbody radiation?

Ps:- I'm a student of 10th grade so please do try to keep the explanation simple.. :-)

## 1 Answer

At the time black body radiation computed with classical electromagnetism, disagreed with the laboratory measurements, giving impossible values for high frequencies. It was called the ultraviolet catastrophy.

The amount of radiation emitted in a given frequency range should be proportional to the number of modes in that range. The best of classical physics suggested that all modes had an equal chance of being produced, and that the number of modes went up proportional to the square of the frequency. But the predicted continual increase in radiated energy with frequency (dubbed the "ultraviolet catastrophe") did not happen. Nature knew better.

Planck's formula, the quantum line in the graph above, agreed with the data and avoided the ultraviolet catastrophe.

• Really nice answer. – Árpád Szendrei Oct 7 '20 at 15:34
• Thanks a lot. I watched a couple of videos on ultraviolet catastrophe and understood the concept.. One thing I did not understand though, is why Planck assumed that energy is quantized? I mean, what does it have to do with blackbody radiation? Could you please explain it to me in a simply way? Thanks in advance – Nisha Prakash Oct 8 '20 at 17:28
• The reason is in the explanation in the first link. Quantizing by hν the available modes, the higher the frequency the less probable to have a radiation. The classical assumption was "equal for all modes" ( seen in graphic on the left) but quantizing leads to fall withhigher ν. read the next pages that describe it simply – anna v Oct 8 '20 at 18:06